A very great many types of folding pocket knives have been developed in which a blade is hinged so as to fold into a handle to cover the sharp blade edge when the knife is being carried and so as to be unfolded into an extended position for use. The edge of the blade opposite the sharp edge is generally slightly exposed and includes a notch or recess for engagement by a fingernail to pull the blade from the stored to the open position.
Such knives may have one or more blades and may have other folding tools such as files, saw blades, scissors, etc. A locking device is often provided to hold the knife in the fully open, use, position and prevent the blade from accidentally folding the sharp blade edge against the user's fingers during use. A button, lever, or similar device is provided to unlock the blade and allow it to be folded.
Opening such a conventional pocket knife is slow and requires two hands, one holding the knife and the other engaging the blade during opening. This can be a significant problem where one hand holds an object to be cut, such as a rope under tension, while the other removes the folded knife from a holster, pocket or the like.
A number of different knives have been developed to open a folding pocket knife more rapidly. The best known is the so-called "switchblade" knife, having a blade spring loaded toward the extended position and a push button latch holding the knife in the folded position. Pressing the button releases the blade, which springs to the open position. While effective, carrying such knives is unlawful in all, or most, states.
Knives exist in which the blade is slidably held in the handle and is extended by sliding a button secured to the blade along the side of the handle to extend the blade. These knives generally have relatively short blades and are prone to jamming of the slide mechanism. Handles on such knives are not well configured to the hand, generally being straight rectangles when a reasonably long blade is to be extended. Further, the mechanisms for locking the blade in housed and extended positions are often not reliable and may release in use.
Thus, there is a continuing need for an improved folding knife that will automatically open during removal of the knife from a holster or pocket, that requires only one hand to open and that does not require any manipulation of the knife during removal other than the simple withdrawal of the knife from a holster, pocket or similar container.